Puppy with digestion problems - Seen three vets, nothing has helped... Advice please!

I have a 7 month old Cockapoo who is happy, hyper and normal in every way...except since the week I brought him home he has had terrible bouts of diarrhea, sometimes lasting weeks at a time. Sometimes its just pudding'ish, other times it is soup, and once or twice blood as well (took him to the vet immediately those times) I got him from a breeder, who has tried to be helpful and has even offered to pay for vet bills (so not from a puppy mill)

He has been tested and treated for every parasite in the book. The only one he came back positive for was Giardia, which he has been on panacure for. Even so, this is his 5th round of panacure since I got him...and nothing seems to be helping. (His most recent stool sample came back negative for Giardia) he is also on Tylosin twice a day... also not helping as far as I can tell...

I have him on a good food (Eaglepack Puppy), but when he gets sick, the vet normally recommends putting him on rice (or oats), chicken broth and Medi-cal Gastro... none of which helps.

Our pup Bodhi is now 12 weeks old. When she was 8 weeks, she was on the skinny side, and the vet suggested we 'beef her up a bit'. She was on Hill's Science diet which was what she was getting at the SPCA.
Our vet suggested we use Medi-Cal development dry and canned for our pup, and then soak the kibble, and mix it with the canned food. So we got the bits we needed, and started to mix it with the science diet stuff to gradually change her over to Medi-Cal.

Well, first of all, after a day she got the trots. So we figured it would be the transition to this 'good' food she's now getting. We kept it up a bit. It didn't help that we had a major heat wave happening, so pup needed more water, was less physically active, etc. We couldn't see whether it was the weather or the food that was causing her stool to become thinner.

Anyway, after a month, we've concluded two things.

1) she gets the trots from the canned Medi-Cal.
2) she gets the trots from soaking her kibble. In fact, she won't eat soaked Medi-Cal development... no matter how long we leave it out for her, or whether it's breakfast, lunch or dinner.
3) she doesn't like the Science stuff soaked either - she'd prefer it dry, with water available at all times.

As long as we were giving her dry kibble, she'd have a solid stool. But she's still not 'beefed up', though she is growing very well.

We're currently changing to Orijen and we love how she's responding to that. Her stool is getting much better, rather than a compacted dry (almost crumbly but not constipated) stool, it's a nice thick paste. The colour is more consistent. It's coming out more consistently too - not in a dollop here, then waddle away, some more bits there...

While the Orijen brand isn't available in all pet stores, it is available in the ones that are closest to us, and it's even available in the local farmer's market. So it's not more 'out of the way' than only being able to get the food at the vet. It's easier for us, in fact. Another part of it is that we're wanting to go raw with the dog, but dh still wants to brush up on his research about it. Until he has, and until he feels comfortable with the information he finds, the Orijen dry food will be a much easier foundation for going raw than a grain-based or grain-containing kibble since both are biologically appropriate.

Unfortunately, Hill's and Medi-cal both are very high in grains IMO. I know that the very first ingredient in every Hill's formula I've ever looked at is corn. Grains will aggravate sensitive stomachs and intestines.

My son's newf had almost constant diarrhea when he was a pup, and he would not gain weight. All his bones stuck out. My vet also treated for Giardia, several times - with no improvement. I had tried a few different foods - so I went back and looked at the ingredients for each of those foods and found that they all had a common ingredient - barley. Suspecting an allergy to barley, I found a high quality food with no barley, and the problem went away. He's still a bit on the lean side (he's almost 5 yrs old now) but he's not scary skinny anymore.